On 13 February 2014, Liang Li <[email protected]> wrote:
> On Thursday, February 13, 2014 4:06:49 PM UTC-5, Bram Moolenaar wrote:
> > lcd wrote:
> >
> > > There is an asymmetry in handling indices for lists
> > > and strings. Lists accept things like lst[n], lst[n1:n2],
> > > lst[n1:-n2], and lst[-n]. Strings accept str[n], str[n1:n2],
> > > str[n1:-n2] (all with the same meanings as the corresponding
> > > operations for lists), but not str[-n]. Negative indices in
> > > strings always return '', which is frustrating. :)
> > >
> > > The patch below makes negative indices behave the same way for
> > > string as they do for lists (but they don't rise exceptions when
> > > out of range):
> > >
> > > :let a = '12345'
> > > :echo a[-1]
> > > 5
> > > :echo string(a[-6])
> > > ''
> > >
> > > Negative indices for strings never did anything useful (at
> > > least as far as I can tell), so this is unlikely to break existing
> > > code.
> >
> > I suppose that would be OK, and useful, to add.
> >
> > Can you also add a test?
>
> Not to derail this, but regarding asymetries -- is there any reason
> why strings aren't treated like arrays of characters, ie, why I can't
> say let str[7]='p' or let str[7:9]='pqr'?
I believe the reason is that you can't do that in Python. :)
Although, the semantics is already slightly different, since str[7:9] in
Vim is actually str[7:10] in Python.
I suppose an argument can be made for implementing full splices for
both lists and strings. E.g. something like list[3:5] = [] would delete
the corresponding elements etc.
/lcd
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